I can verify that Algoriddim DJAY does indeed fully work on Catalina, including playlist support in the new music app . It was mentioned in their forum that they are already using the API and I upgraded to Catalina on my 2012 MacBook Air i7 I use for DJing....I was able to use the music app to modify a playlist, and changes appeared in DJAY when I relaunched it (or you can reload the libraries from the menu).
I will veryify, and I posted this in the forum, that the playlists are slow to load when you FIRST launch DJAY, and the first song you attempt to cue, or load on a deck will give you a brief spinning beach ball, but then it works as expected moving forward.
Of course, I did a complete backup right before I upgraded...I don't have a gig for a couple weeks so I figured now would be a good time to play with it, and can roll back if I have to....but for DJAY, all good.
For those that have not tried DJAY...it is amazing app, for iPhone, iPad, MacOS and Windows...with Spotify integration as well. It supports all the major Controllers, and you can Midi map any that it does not support natively. The latest iPad version also allows you to use the new FILES option in iOS 13 and access music from a HD or memory card. Really...if looking for a general purpose, GOOD DJ program, give DJAY a try...it is amazing to have people make requests and just be able to search Spotify right from within the program and pull the song right on a deck, you can then Beat Match it, Scratch it, etc etc etc. Pretty amazing to fire it up on my iPhone and be able to access all my Spotify playlists and actually DJ...
Now, please understand I totally get old school Vinyl DJing....and that is truly an art and I give full props to those that still use Vinyl, as well as Vinyl based control records for Serrato, Virtual DJ etc etc (BTW DJAY works with Vinyl as well)....but for my needs, and for the events I do...DJAY is amazingly good, and they have always supported quick updates for OS and iOS updates etc.